Inference of stratospheric aerosol composition and size distribution from SAGE II satellite measurements

Abstract

In this paper the authors present a method that can be used to infer stratospheric aerosol composition and size distribution, based on the water vapor concentration and aerosol extinction measurements from the satellite instrument of the Stratospheric Aerosol and Gas Experiment (SAGE II) and the associated temperatures provided by the National Meteorological Center (NMC). To infer the chemical composition, the aerosols are assumed to be sulfuric acid‐water droplets. The equilibrium acid weight percentage and refractive index at the SAGE II aerosol wavelengths can then be estimated by using the SAGE II‐observed water vapor and the associated temperatures. To infer the aerosol size distribution, a modified Levenberg‐Marquardt algorithm is adopted for determining model size distribution parameters in the least squares sense, based on the SAGE II‐observed multiwavelength aerosol extinctions. Both single‐mode lognormal and modified gamma representations are employed in the analysis. One of the most significant conclusions from this analysis is a determination of the information content of the SAGE II multiwavelength aerosol extinctions with respect to stratospheric aerosol size distributions. It is concluded that the best aerosol size information is contained in the aerosol radius range between approximately 0.25 and 0.80 μm.